Effect of Placement Technology on the Bond Strength Between Two Layers of Self-Compacting Concrete
Abstract
:1. Introduction
2. Materials and Methods
2.1. Concrete Mixture
2.2. Test Specimens
2.3. Test Procedures
2.3.1. Fresh Mix Property Tests
2.3.2. Hardened Concrete Tests
2.3.3. Test of the Bond Strength in the Multilayer Casting of SCC
3. Results
3.1. Fresh Mix Properties and Concrete Strength
3.2. Bond Strength Between Two Concrete Layers
3.3. Effect of Multilayer Casting Variants on the Bond Strength
3.4. Bond Failure Mechanism
4. Discussion
5. Conclusions
- In general, a reduction in bond strength between the layers was noted as the delay time between layers was extended. The most significant decrease was obtained in the case of Variant A in the entire range of research. For the delay times of 30, 45, and 60 min, the average reduction of bond strength in relation to the control sample for Variant A was 13%, 26%, and 36%, respectively, and for Variant B, was 8.8%, 7.5%, and 13%, respectively. In the case of Variant C, hardly any change was obtained for the 30 min delay time and for the 45 and 60 min delay times, the decrease was 6% and 5%, respectively;
- The analysis of the failure surface condition showed that in Variant A, the proper mixing of subsequent layers is limited. This resulted from the structural buildup at rest of the first layer and the lack of a sufficient impact required for its plasticization. The larger the area of the intact surface of the first layer, the lower the bond strength between two layers. Variants B and C of placement technology caused the previously laid mixture to properly restore a plastic state on the surface, thus enabling its efficient mixing with the new one. In these technologies, no visible discolorations and traces were observed at the contact of layers—the so-called lift line;
- Based on the investigations, it is recommended that subsequent layers of SCC be placed so that the previously laid mix can be superficially plasticized, thus facilitating its bonding to the new layer. It is suggested that the method of either mechanical surface mixing or increasing the height from which the next batch of SCC is poured should be applied. If the variant of an increased casting height is adopted, the mix should be dropped over the entire surface of the component without a fixed single casting point.
Author Contributions
Funding
Conflicts of Interest
References
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Constituent Materials | Composition [kg/m3] |
---|---|
Cement CEM II/B-V 32.5R | 360 |
Water | 160 |
Sand 0–2 mm | 700 |
Gravel aggregate 2–8 mm | 350 |
Gravel aggregate 8–16 mm | 350 |
Fly ash | 90 |
Superplasticizer | 2.8 |
Mix Batch | Delay Time | Slump-Flow (mm) | Slump-Flow Class | Slump-Flow Time T500 (s) | Viscosity Class | Fresh Visual Stability Index | L-Box Ratio | L-Box Class |
---|---|---|---|---|---|---|---|---|
SCC-I | t = 0 min | 685 | SF2 | 1.7 | VS1 | 0 | 0.90 | PL2 |
SCC-II | t = 0 min | 710 | SF2 | 1.9 | VS1 | 0 | 0.92 | PL2 |
SCC-II | t = 15 min | 695 | SF2 | 2.1 | VS2 | 0 | 0.89 | PL2 |
SCC-II | t = 30 min | 680 | SF2 | 2.5 | VS2 | 0 | 0.87 | PL2 |
Mix Batch | Compressive Strength | Splitting Tensile Strength | ||
---|---|---|---|---|
fcc (MPa) | SD 1 (MPa) | fct,sp (MPa) | SD (MPa) | |
SCC-I | 56.5 | 1.808 | 2.97 | 0.214 |
SCC-II | 53.3 | 2.292 | 3.18 | 0.204 |
Multilayer Casting Variant | Delay Time between Successive Layers | Reduction Rate in Bond Strength (MPa/min) | |||||||
---|---|---|---|---|---|---|---|---|---|
t = 0 min 1 | t = 30 min | t = 45 min | t = 60 min | ||||||
fct,sp (MPa) | SD 2 (MPa) | fct,sp (MPa) | SD (MPa) | fct,sp (MPa) | SD (MPa) | fct,sp (MPa) | SD (MPa) | ||
A | 3.08 | 0.210 | 2.67 | 0.284 | 2.29 | 0.278 | 1.97 | 0.280 | 0.0186 |
B | 2.81 | 0.226 | 2.85 | 0.216 | 2.68 | 0.201 | 0.0068 | ||
C | 3.12 | 0.172 | 2.89 | 0.213 | 2.93 | 0.218 | 0.0025 |
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Dybeł, P.; Kucharska, M. Effect of Placement Technology on the Bond Strength Between Two Layers of Self-Compacting Concrete. Materials 2020, 13, 3330. https://doi.org/10.3390/ma13153330
Dybeł P, Kucharska M. Effect of Placement Technology on the Bond Strength Between Two Layers of Self-Compacting Concrete. Materials. 2020; 13(15):3330. https://doi.org/10.3390/ma13153330
Chicago/Turabian StyleDybeł, Piotr, and Milena Kucharska. 2020. "Effect of Placement Technology on the Bond Strength Between Two Layers of Self-Compacting Concrete" Materials 13, no. 15: 3330. https://doi.org/10.3390/ma13153330